We will continue our investigation of peripheral oculomotor mechanisms by comparing the fatigability of extraocular muscles and correlating this property with their respective functional roles. Variations in the relative content and distribution of fiber types in these muscles will be determined by light and electron microscopy. Extraocular muscle response to neuromuscular depolarizing agents will be studied by microscopic examination of singly-innervated, multi-innervated and denervated muscle fibers, fixed in situ during administration of succinylcholine and stained to reveal the location and distribution of endplates or residual cholinesterase activity. Differential response to intravenous succinylcholine of whole muscles will be measured by strain gauge recordings and compared to the effects of electrical stimulation. Additionally, we plan to identify single motor units by intracellular recording and stimulation, and provide a complementary morphological study of cellular organization in the abducens nucleus with respect to the size of its emergent axons.